The present invention relates to antennas for radio frequency telemetry applications, and more particularly to a system and method for directing an adaptive antenna array in the direction of an aircraft in flight in order to establish a radio frequency (RF) communication link between the aircraft in flight and a receiver.
A significant problem encountered in the art of in-flight telemetry relates to the frequency and, more importantly, the power at which telemetry devices can transmit RF signals. Until the enactment by the Federal Communications Commission (FCC) of Part 15.247 of the FCC Rules and Regulations, aircraft telemetry systems were primarily limited to the VHF band (174-216 MHz), and could only operate at very low transmission powers of less than 0.1 milliwatts (mW) (FCC Part 15.241). This restriction on the transmission power has significantly limited the transmission range (i.e., the maximum distance between the transmitter and the receiver) of airborne telemetry devices.
Directional antennas, such as those used in conventional RF communications receivers have forward lobes or beams that represent areas of maximum receiver gain. The receiver gain is generally highest when these beams are positioned in the direction of the signal source. Such antennas also typically have nulls, or areas of lowest gain, e.g., at their sides. Nulls can be positioned to desensitize reaction to unwanted signals, based on their direction of arrival. The position of lobes and nulls in such antennas is commonly fixed upon installation and remains fixed over time.
However, the position of an aircraft in flight is constantly changing with respect to a given ground based receive antenna. Accordingly, a problem exists in the telemetry arts with respect to establishing reliable telecommunication links between an aircraft in flight and a ground based receiver, especially under circumstances in which the output power of the transmit antenna on board the aircraft in flight is limited.
The present invention overcomes this problem by providing a system and method for electronically steering the main lobe of a receive antenna array pattern in the direction of an aircraft in flight while simultaneously minimizing the receiver sensitivity to signals from other directions, including interference signals from other directions and background thermal noise from other directions. In an exemplary embodiment of the invention, a system and associated method for directing a main receiving lobe of an adaptive antenna array toward an aircraft in flight comprises an aircraft position vector calculator and an antenna weight vector generator. The aircraft position vector calculator receives aircraft position information for an aircraft from an aircraft tracking means such as an aircraft tracking service. The aircraft position vector calculator calculates an aircraft position vector g, for selected aircraft in flight, and provides position vector g at an output. The antenna weight vector generator receives aircraft position vector g from the aircraft position vector calculator and generates an antenna weight vector w, based on position vector g. The weight vector generator provides antenna weight vector w to the antenna elements of the adaptive antenna array such that a receiving lobe of the adaptive antenna array is directed toward the aircraft in flight.